Typical solder joints have some shortcomings including solder joint fatigue, pad cratering, and head in pillow defects. The solder joint fatigue can be caused by the CTE (Coefficient of thermal expansion) mismatch between components and PCB (Printed Circuit Board). Pad cratering can be caused by shocks and vibrations during transportation, especially for large components assembly. Head in pillow defects can happen during a reflow process due to warpage of packages at a reflow temperature.
To mitigate the above problems, various solutions are typically used. For example to mitigate the solder joint fatigue problem, lower performance organic substrate or HiCTE substrate are used to match the CTE between the substrate and PCB. Organic substrates provide inferior electrical performance as compared to ceramic substrate. To reduce pad cratering, cushions to the system packaging are added to reduce the shock impact during transportation, which results in increased costs. X-rays have been used to screen the assembly to examine the occurrences of head-in-pillow (HiP); however, it is very challenging for x-ray to screen out all the HiP defects.